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Program: Arrow Gear’s Advanced Design and Development Assistance Capabilities


Developing the Contact Pattern through Computer Modeling – Details of the Process

In this chapter, we’ll present the details involved in the process of designing the contact pattern through computer modeling and how the software integrates with the machine tools.

To begin, this is a summary printout of a TCA study. This particular TCA is from the PW6000 upper tower gearset.

For the purpose of illustration, we will be looking at the concave gear and addressing the loaded TCA phase of the design work, were the various displacement conditions were accounted for.

Here you can see the contact pattern design that we created to meet the load requirements and the different displacements that the gear sets would encounter.

The different displacements which were presented to us are as shown. At 3,140 inch pounds of torque, we could have the possibility of the pinion moving above the gear by 13 thousandths, the pinion going into mesh 13 thousandths and the gear out of mesh by 12 thousandths. We have another set of circumstances where it’s nearly 2 thousandths offset, pinion into mesh almost 23 thousandths and the gear is near stationary. We have another set of circumstances where there is nearly 2 thousandths worth of offset, pinion into mesh almost 29 thousandths and the gear into mesh 18 thousandths.

Our job was to design a contact pattern that would stay on the tooth, have an acceptable shape and size, never running to the end, and meet all these different displacement conditions that the gears would experience under their normal operation.

The contact pattern that we designed then met those requirements as shown. Under each requirement, you can see what the loaded TCA design contact pattern would produce as a contact.

If you were to take all these contact patterns and overlay them or combine their areas of contact, you would, in essence, have a depiction of what the load zone will be for this gearset while it is in operation and encounters all of these different displacements at 3,140 in pounds of torque.

In addition to each one of the different displacements on the contact study, we’ll also look at the various pressures that are occurring along the path of engagement. As the tooth comes into mesh, the path of engagement starts here. It then rolls through mess and exits at this end.

Given a load of 3,140 inch pounds of torque, this table shows what the surface pressure is at the start of engagement all the way through to the end of engagement. You’ll see that the pressures at the start of engagement are low, which is a result of tooth sharing - due to the high contact ratio. The pressures then start to climb, and will reach a peak of 238,000 pounds per square inch in the center of the tooth. The pressures will then diminish – finally falling to nearly 84,000 where this tooth has exited from mesh.